In recent years, the communication speed of optical communication has been increasing, which requires an optical communication module that is higher in communication speed, smaller in size, and lower in power consumption. Therefore, an integrated optical communication module (hereinafter, referred to as “integrated optical module”) that is small in size and high in communication speed has been developed. In such an integrated optical module, a plurality of light receiving elements is mounted, a wavelength-multiplexed light beam output from one fiber is demultiplexed into a plurality of light beams having different wavelengths to cause the light receiving elements to receive the light beams, and an optical signal is converted into an electric signal by each of the light receiving elements.
For the conventional optical communication module, one light receiving element is provided for one optical communication module, and optical axis adjustment of a light beam output from an optical fiber is performed for the one light receiving element, and the optical communication module and the optical fiber are fixed at a position where a current value of an electric signal resulted from converting an optical signal in the light receiving element becomes optimum. On the other hand, optical axis adjustment is required for the integrated optical module to achieve a configuration where a plurality of light receiving elements is mounted in one integrated optical module, and a wavelength-multiplexed light beam output from an optical fiber is demultiplexed into a plurality of light beams having different wavelengths to cause each of the light receiving elements to receive a corresponding one of the plurality of light beams. Therefore, the optical axis adjustment needs to be performed by the number of light receiving elements mounted in the integrated optical module.
On the other hand, in the method described in Patent Document 1, an optical demultiplexer that includes a plurality of wavelength filters and demultiplexes an incident optical signal into a plurality of signal light beams having different wavelengths is prepared, a position of the optical demultiplexer is determined based on a difference between a reference angle and a design angle with reference to an angle perpendicular to an optical axis of an external light source for optical axis adjustment, then an optical signal received by each light receiving element is measured, and the position of the optical demultiplexer is fine-adjusted.